Frequency multiplier



May 22, 1955 L J. MAYER FREQUENCY MULTIPLIER 2 Sheets-Sheet 2 Filed April 16, 1952 INVENTOR. HDW/ J. /VHYEE FREQUENCY MULTIPLIER Ludwig J. Mayer, Dayton, Ohio, assigner to the United States of America as represented by the Secretary -of the Air Force Application April 16, 1952, Serial No. 282,668

4 Claims. (Cl. 315-6) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to frequency multipliers and has as its object a frequency multiplier for the generation of ultra high frequencies in which the order of multiplication is relatively high and in which the direct to radio frequency current conversion eiciency is also relatively high.

The multiplier consists essentially of a velocity modulated or klystron frequency multiplier to which has been added a device, termed a phase shutter, to admit electrons to the buncher or velocity modulating element only during that part of the fundamental frequency cycle that will produce the most nearly ideal bunching of electrons from the standpoint of harmonic content.

The multiplier will be described in more detail in connection with two possible embodiments thereof shown in the accompanying drawings, in which- Fig. 1 shows one embodiment of the invention in which the proper phase relation between the electrons admitted to the buncher and the fundamental frequency voltage at the buncher gap is obtained by introducing an appropriate phase shift between the phase shutter and the buncher;

Fig. 2 shows another embodiment of the invention in which the above mentioned proper phase relation between electrons and voltage wave is obtained by an appropriate spacing of the buncher and phase shutter; and

Figs. 3 and 4 graphically illustrate the operation of Figs. l and 2.

Referring toFig. l, cathode 1, buncher or velocity modulator 2 comprising resonant cavity 3 tuned to the fundamental frequency and velocity modulating gap Gv defined by grids 4 5, catcher 6 comprising resonant cavity '7 tuned to the desired harmonic and an energy extracting gap defined by grids 8-9, and anode 10'are similar to the corresponding elements of a conventional klystron frequency multiplier. To these has been added the phase shutter 11 consisting of cavity 12, resonant at the fundamental frequency, having a grid 13 which together with the emitting surface of cathode 1 defines a beam density modulating gap Gd. Input energy at the fundamental frequency is applied-over transmission line 14 to coupling and phase shifting network 15 which supplies energy to cavity 12 by means of line 16 and coupling loop 17 and to cavity 3 by means of line 18 and coupling loop 19. Network 1S delays the phase of the energy applied to cavity 3 relative to that applied to cavity 12 by an amount to be defined later. This network may be any of the known types suitable to the frequencies involved such as a wave guide or coaxial.

transmission line. Voltage source 20 provides a bias potential for grid 13 while voltage sources 21 and 22 maintain grids 4, 5, S and 9 and anode 10 positive relative to the cathode. g

The principle of operation of Fig. l is as follows: The

Ynted States Patent 2,747,129 Patented May 22, 1956 bias voltage E20 is greater than the cut-ott voltage of grid 13 by the proper amount to prevent electron emission from the phase shutter 11 except during intervals of approximately 3/81r which are centered with respect to the center or 1r/2 points of the positive half-cycles of the voltage wave at the gap Ga. This is illustrated at (b) in Fig. 3. As a result one bunch of electrons 25 is emitted by the phase-shutter during each cycle of the fundamental frequency wave at Gs, as illustrated at (c) in Fig. 3.

The fundamental frequency wave across velocity modulating gap Gv is illustrated at (a) in Fig. 3. It is desired that the electrons from the phase-shutter, which form the bunches 25, pass through the gap Gv during that part of the fundamental frequency cycle extending from approximately 1r/4 to 1r/ 8. This is accomplished in Pig. 1 by an appropriate phase delay, by phase shifter 15, of the voltage at Gv relative to that at Gd. Neglecting the transit time of the electrons between the two gaps the proper phase delay is 9/l61r as shown in Fig. .3. If the transit time is not negligible the transit angle of the electrons should be added to 9/161r in order to arrive at the correct phase difference between the voltages at Gv and Gd. In any event the proper value should lie between 9/l61r and 3/41r.

Each electron in passing through gap Gv has its velocity modified in accordance with the amplitude and polarity of the voltage across Gv during its transit. Therefore electrons of various velocities are emitted from Gv and these collect in the drift space S to form sharp bunches of electrons 26 as shown in Fig. 3 (c). Electron bunches 26, in passing through the gap between grids 8 and 9, excite the resonant circuit of the catcher 6 which is tuned to a `harmonic of the fundamental frequency. Since onlyry one bunch 26 occurs for each cycle of the fundamental frequency electrons pass through the catcher gap only' during the decelerating phase of the radio frequency voltage. The direct current to radio frequency current conversion elliciency is therefore high.

Fig. 2 shows another method of eifecting passage of the electrons emitted by the phase shutter 11 through the gap Gv during the interval -1r/ 4 to 11-/8 of the voltage wave at Gv. In this arrangement the buncher 2 is inverted with respect to its position in Fig. l and the resonant circuits of the buncher and phase-shutter are excited by energy of funamental frequency applied thereto in the same phase by a suitable coupling network 15. The desired phasing of the electrons relative to the radio frequency voltage across gap Gv is attained by making the distance d between gaps Gv and Gd of such value that the transit angle of the electrons between the two gaps equals 9/ 1611-. This relationship is shown graphically in Fig. 4. The required distance d is given approxi-V mately by the following expression.

cm., in which E=direct voltage of grids 4 5 f=fundamental frequency The theory underlying the design of the above described frequency multipliers is as follows: With a sequence of sharp electron beam pulses occurring at the from the buncher by a voltage rise across the buncher gap in accordance with P wherein a and Eu=voltage across gap of buncher Eni-direct voltage at which electrons enter buncher e=electron charge m=electron mass It would be diflcult to create such a voltage rise periodically at a frequency high enough to be suitable as fundamental frequency in a multiplier for the generation of very high frequencies. However, the shape of an ordinary lsine wave in the vicinity of the zero point preceding a positive half-cycle extending from 1r/4 to 1r/8 is a good approximation of the above ideal shape for creating very sharp beam pulses. Hence an electron beam sent through a velocity modulation gap only during the above interval of the fundamental frequency wave at the gap will be phase-focussed nearly ideally to very sharp electron pulses which are able to excite harmonics of a very high order.

Restricting the current flow to the above defined intervals can not b e done directly as it is only possible to open the current flow symmetrically around the positive maximum of the sine wave, or in other words, around vr/ 2. Therefore, two control gaps or grids must be used, the voltages at which have to be apart in phase slightly less than 3/41r or which must be spaced apart so that the transit time between the two provides the required delay. The rst control unit, the phase shutter 11, of Figs. l and 2, operates mainly as a density controlling device opening the gate for the electrons only during a phase interval of 3/81r which is symmetrical to 1r/2. After a phase delay of something less than 3/41r, produced in Fig. l by the delay network v1,5 and in Fig. 2 by proper spacing of the buncher and phase-shutter gaps, the electron beam, now already pulsed, must be subjected to a velocity modulation which results in the formation at the catcher, after traversing the drift space, of much narrower bunches `out of the relative wide bunches admitted to the velocity modulator. The narrow bunches are capable of generating harmonics of a high order in the catcher.

I claim:

1. A klystron frequency multiplier comprising a cathode, a buncher having a velocity modulating gap and a resonant circuit associated with said gap and tuned to a fundamental frequency, a catcher having an energy extracting gap and a resonant circuit associated with said gap and tuned to a harmonic of said fundamental frequency, and an anode, said cathode, buncher, catcher and anode being aligned so that electrons pass from said cathode through the gaps of said buncher and catcher in succession to said anode, means for applying energy at said fundamental frequency to the resonant circuit of said buncher whereby a sine. Wave of voltage of said fundamental frequency is established across the gap of said buncher, and means for blocking the dow of electrons from the cathode to the velocity modulating gap of said buncher except duringrv that part of the cycle of the voltage across said gap extending` approximately from #1r/4 to 1r/8 radians, said last named means comprising a grid positioned between said cathode and the entrance to the gap of said buncher, a resonant circuit tuned to said fundamental frequency associated` with said grid and cathode, means for applying energy at said fundamental frequency to said resonantI circuit whereby a, sine Wave of voltage. at said fundamental frequency is established 4 t between said grid and cathode, means for biasing said grid negative relative to said cathode to such an extent that electron flow from said cathode to the gap of said buncher is cut off except during an angular interval of approximately 3/81r radians, relative to said fundamental frequency, which is centered with respect to the midpoint of the positive half-cycle of said sine wave of voltage between said grid and cathode, and means for timing the entry into said modulating gap of the electrons passed by said grid during said 3/81r interval so that said entry occurs during that part of the cycle of the voltage across said modulating gap extending from 1r/4 to 1r/8 radians.

2. A klystron frequency multiplier comprising a cathode, a buncher having a velocity modulating gap and a resonant circuit associated with said gap and tuned to a fundamental frequency, a catcher having an energy extracting gap and a resonant circuit associated with said gap and tuned to a harmonic of said fundamental frequency, and an anode, said cathode, buncher, catcher and anode being aligned so that electrons pass from said cathode through the gaps of said buncher and catcher in succession to said anode, means for applying energy at said fundamental frequency to the resonant circuit of said buncher whereby a sine wave of voltage of said fundamental frequency is established across the gap of said buncher, a grid situated between the gap of said buncher and said cathode and close to the entrance to said gap, a resonant circuit connected between said grid and said cathode and tuned to said fundamental frequency, means for energizing said last-named resonant circuit at said fundamental frequency whereby a sine wave of voltage at said fundamental frequency is established between said grid and cathode, means for biasing said grid negative relative to said cathode to such an extent that electron ow from said cathode to the gap of said buncher is. cut oif except during an angular interval of approximately 3/811 radians relative to said fundamental frequency, which interval is centered with respect tothe mid-point of the positive half-cycle of said sine wave of voltage between said grid and cathode, and means for delaying the phase of the sine wave of voltage at the gap of said buncher relative to the sine wave of voltage between said grid and cathode by an angle of approximately 9/l61r radians.

3i A klystron frequency multiplier comprising a cathode, a buncher having a velocity modulating gap and a resonant` circuit` associated with said gap and tuned to a fundamental frequency, a catcher having an energy extractingV gap and a resonant circuit associated with said gap andl tuned to a harmonic of said fundamental frequency, and an anode, said cathode, buncher, catcher andkv anode. being aligned so that electrons pass from said cathode through the gaps of said buncher and catcher inv succession to said anode, means for applying energy at saidy fundamental frequency to the resonant circuit of said buncher whereby a sine wave of voltage of said fundamental frequency is established across the gap of said buncher, a grid situatedbetweenY the gap of said buncher and said cathode, a resonant circuit connected between said` grid andV said cathode and tuned to said fundamental frequency, means for energizing said last named resonant circuit at said fundamental frequency whereby a sine wave of voltage at said fundamental frequency is established between said grid and cathode, means for biasing` said grid negative relative to said cathode totsuch an extent that electron flow from said cathode to the. gap. ofl said buncher is cut off except during an angular interval ofapproximately 3/8vr radians relative toV said fundamental frequency, which interval isV centered` with respect to theV midpoint of the positive half-cycle of saidl sine wave of` voltage between said grid and cathode, and means spacing the gap of said buncher from said cathode by such a distance that the electrons passingt through` said grid during the said 3/ 811- interval pass through the gap of said buncher during that part of the cycle of the voltage across said buncher gap extending approximately from 1r/4 to 1r/8 radians.

4. A klystron frequency multiplier comprising a cathode, a buncher having a velocity modulating gap and a resonant circuit associated with said gap and tuned to a fundamental frequency, a catcher having an energy extracting gap and a resonant circuit associated with said gap and tuned to a harmonic of said fundamental frequency, and an anode, said cathode, buncher, catcher and anode being aligned so that electrons pass from said cathode through the gaps of said buncher and catcher in succession to said anode, means for applying energy at said fundamental frequency to the resonant circuit of said buncher whereby a sine wave of voltage of said fundamental frequency is established across the gap of said buncher, a grid situated between the gap of said buncher and said cathode, a resonant circuit connected between said grid and said cathode and tuned to said fundamental frequency, means for energizing said last 20 2,616,038

named resonant circuit at said fundamental frequency whereby a sine wave of voltage at said fundamental frequency is established between said grid and cathode, means for biasing said grid negative relative to said cathode to such an extent that electron ow from said cathode to the gap of said buncher is cut oi except during an angular interval of approximately 3/81r radians relative to said fundamental frequency, which interval is centered with respect to the midpoint of the positive half-cycle of said sine wave of voltage between said grid and cathode, means establishing an inverse phase relation between the voltage across the gap of said buncher and the voltage between said grid and cathode, and means spacing the gap of said buncher from said cathode by such a distance that the transit angle of the electrons thereacross is approximately 9/161r radians.

References Cited in the le of this patent UNITED STATES PATENTS Re. 22,990 Hansen et al Mar. 23, 1948 2,305,883 Litton Dec. 22, 1942 2,466,704 Harrison Apr. 12, 1949 2,494,568 Lundy Jan. 17, 1950 Hansen et al. Oct. 28, 1952 FOREIGN PATENTS 578,270 Great Britain June 21, 1946 960,254 France Apr. 14. 1950 

